While the pathogenesis of aging spots, etc., is partially unknown, it is generally considered that abnormalities of hormones or the stimulation by ultraviolet rays from sunlight causes the formation of melanin pigments and the pigments are abnormally deposited in the skin. The melanin pigments which cause pigmentation of the skin are produced in melanin-producing granules (melanosomes) within melanin cells (melanocytes) between the epidermis and the hypodermis, and the produced melanin diffuses to adjacent cells by osmosis.
The biochemical reaction in melanocytes is presumed to be as follows. Namely, the production process of melanin pigment is that tyrosine, an essential amino acid becomes dopaquinone by the action of the enzyme, tyrosinase, and the dopaquinone is converted to black melanin by enzymatic or non-enzymatic oxidation activity.
Various whitening agents for controlling the occurrence of the aforementioned melanin pigments, comprising extracts derived from plants have been conventionally developed in the anticipation that such extracts are safe and mildly irritating to the skin (refer to, for example, Patent Documents 1 to 4).
However, it is well known that active oxygen is generated by ultraviolet rays. Among active oxygen species, free radical type active oxygen reacts with an oxidizable substrate such as lipid, inducing an oxidation chain reaction. Therefore, active oxygen which can become free radicals amplifies damage to body tissue such as skin.
The skin is always exposed to oxygen and ultraviolet rays, and thus, is the tissue which has the greatest oxidative stress damage by free radicals. Recently, it has been considered that a variety of active oxygen species generated by ultraviolet rays cause the peroxidation of sebum and lipid, protein degeneration, enzyme inhibition, etc., and thereby, the inflammation, etc., of the skin is induced over the short term, and aging, cancer, and the like are caused over a prolonged period of time.
Further, it is considered that active oxygen and peroxidized lipids are associated with skin diseases such as atopic dermatitis, contact dermatitis, and psoriasis. In this way, active oxygen (free radicals) is deeply involved in aging of the skin and skin diseases.
Substances having the ability to scavenge free radicals can control and terminate free radical chain reactions, and correspond to, for example, substances referred to as antioxidant agents.
Therefore, skin external preparations comprising an antioxidant agent are anticipated to have an effect of prevention and improvement of aging in the skin (for example, aging spots, wrinkles, sagging skin, etc.) caused by photooxidative stress. Further, the skin external preparations can be anticipated to have an effect of prevention and improvement, as skin external preparations for various skin diseases associated with free radicals.
Vitamin E and vitamin C which are known as antioxidant agents are in vivo free radicals scavenger antioxidant substances. Further, the synthetic antioxidant substances of BHT and BHA are also known. Furthermore, as conventional antioxidant agents derived from plants, extracts of Chinese mushrooms, enoki mushrooms, shimeji mushrooms, maitake mushrooms, matsutake mushrooms, Ganoderma lucidum, Daedalea dickinsii, Pholiota nameko, and other basidiomycetes have been reported (Patent Documents 6 to 8). Furthermore, antioxidant agents consisting of extracts of a plant belonging to the genus Verbascum of the family Scrophulariaceae (Patent Document 9) and antioxidant agents consisting of extracts of a plant belonging to the genus Cordia of the family Boraginaceae (Patent Document 10) have been reported.
Further, Patent Document 5 mentions a solvent extraction of Psilotum nudum belonging to the family Psilotaceae as a plant extract comprising apigenin or amentoflavone. Patent Document 5 shows no data that this plant extract has a melanogenesis stimulation activity, thus, in Patent Document 5, the function of the solvent extraction of Psilotum nudum itself is unclear. The present invention relates to the melanogenesis-inhibitory action and the free radical scavenging-type antioxidation activity due to the Psilotum extract. Thus, the description of Patent Document 5 and the contents of the present invention are completely different.